Conventionally, as an immunogen required for production of anti-HbA1c antibodies, HbA1c itself has been generally used. HbA1c has a structure similar to that of hemoglobin A0 (hereinafter abbreviated as HbA0) which constitutes 90% of the total amount of hemoglobin. Whereas HbA0 has no sugar chain at the N-terminus of its β chain, HbA1c has a fructose binding to the N-terminus of its β chain. This is the only difference between HbA0 and HbA1c. Therefore, most of the antibodies which are produced using HbA1c itself as an immunogen can also recognize HbA0. Among the antibodies for hemoglobin, there are only a small number of antibodies capable of recognizing only HbA1c. Conventionally, such a group of antibodies have been screened for those that bind to HbA1c.
Such screening work is labor-intensive and costly. Therefore, it may be conceived to use an epitope capable of recognizing only HbA1c. However, in most cases, an epitope alone does not have sufficient antigenicity or immunogenicity in production of an antiserum or antibodies. Therefore, an animal is immunized with an epitope in conjunction with an adjuvant or a carrier. However, immunization of an animal with a carrier and an epitope is conventionally labor-intensive and is not necessarily efficient to obtain an intended antiserum or antibodies, and is also costly. Moreover, acquisition of an intended antibody depends on probabilistic factors, and the above-described method cannot be said to be reliable. No monoclonal antibody without cross reactivity to HbA0 has been obtained, and there has been conventionally no established method with which such a monoclonal antibody can be reliably and simply produced.
In order to solve the above-described problems, an object of the present invention is to provide a peptide fructose compound and a protein conjugate which are immunogens capable of producing anti-HbA1c antibodies, preferably only anti-HbA1c antibodies, where the probabilistic factors are removed and the antibodies have no cross reactivity to HbA0. Another object of the present invention is to provide an antiserum or antibodies produced using such a peptide fructose compound or a protein conjugate. Still another object of the present invention is to provide a method of producing an antibody-producing cell capable of supplying an antibody specific to HbA1c and without cross reactivity to HbA0 and capable of stably supplying such an antibody for future use, where the probabilistic factors are removed.